1. Field of the Invention
The present invention relates in general to methods of directing spacecraft payloads, and in particular to a method and apparatus for estimating antenna directivity for a reconfigurable phased array antenna on a spacecraft in order to reconfigure the antenna within a specified time limit.
2. Description of the Related Art
Satellite systems are widely used to transmit information to many ground users. In satellite-based communication, it is desirable to transmit information to ground-based users in certain areas, but not the ground-based users in other areas. This is accomplished with the use of “shaped beams” that concentrate the energy of the transmitted signal to a limited terrestrial area, known as a coverage area for the antenna.
It may be desired to optimize the use of such shaped beams, based on external factors. For example, it may be desired to redistribute the power radiated by the satellite's antenna dynamically based on weather conditions. For example, higher power may be required to compensate for rainy weather conditions in certain portions of the coverage area, while lower power can be used for sunny weather conditions in other portions of the coverage area. If power can be dynamically shared or redistributed between rainy and sunny portions of the coverage area, the overall power of the antenna can be utilized more efficiently. As a result, the satellite will provide less power for dynamic power distribution than for static power distribution.
Weather-driven dynamic power control is a great method to conserve resources and reduce costs on satellites. However, satellites still need to provide good service to those portions of the coverage area receiving lower power as the weather changes. The challenge is to calculate a reasonable power distribution among many possible power distributions and then re-configure the antenna to use the reasonable power distribution. Moreover, the reasonable power distribution over the coverage area and the reconfiguration of the antenna must be calculated within a specified time limit, which may be governed by how fast the weather conditions are updated.
Preferably, the antennas on the satellite are dynamically re-configurable in order to perform the dynamic power re-distribution. One type of re-configurable antenna is a phased array antenna with multiple elements. The phase distribution of the antenna elements controls the radiated antenna pattern, and consequently changes the power distribution over the coverage area.
The process of acquiring the phase distribution of the antenna elements is a time consuming task, e.g., 8-15 minutes per phase distribution optimization. The phase distribution of the elements in the phased array antenna must be adjusted in order to generate an antenna pattern that distributes the power on a coverage area with the best service to the users. The power distribution over the coverage area is described as the antenna directivity profile.
However, the optimization of the phase distribution may include inappropriate or impossible requests (antenna directivity profiles) for phase adjustments. In order to enhance such optimizations, such inappropriate or impossible requests should be eliminated from consideration to speed up the process. The present invention provides a system to perform this function.